Touch of Death tracker for Shadowlands.
When you select a target, you will see a number between 1-100. When the target is at full health, the number is 100. As the target loses health, the number decreases. When it reaches 0, the Touch of Death icon will show up and begin to glow, indicating that ToD is now usable.
The countdown is linear as they begin to lose health, so as it ticks towards 0 you have a sense of how soon you can use ToD.
When ToD is on cooldown it will instead show the cooldown remaining.
It works regardless of which active condition will be triggered first (player HP > target HP or target HP < 15%). Only works on attackable targets so you will need to target something hostile.